There is currently interest in the detergent industry in concentrated detergent products. These products provide advantages to the consumer, who has a product which can be used in lower amounts and is more easily stored, and to the producer and intermediates, who have lower transportation and warehousing costs. A major difficulty, though, is finding an inexpensive and efficient way to produce a high active detergent particle for inclusion in a concentrated detergent product. By "high active" is meant greater than about 50% active.
The traditional method for producing detergent granules is spray drying. Typically, detergent ingredients such as surfactant, builder, silicates and carbonates are mixed in a mix tank to form a slurry which is about 35% to 50% water. This slurry is then atomized in a spray drying tower to reduce moisture to below about 10%. It is possible to compact spray dried particles to make dense detergent granules. See U.S. Pat. No. 4,715,979, Moore et al., issued Dec. 29, 1987. However, the use of spray drying to make condensed granules has some disadvantages. Spray drying is energy intensive and the resulting granules are typically not dense enough to be useful in a concentrated detergent product. Spray drying methods generally involve a limited amount (less than 40%) of organic components such as surfactant for environmental and safety reasons.
One way to reduce the energy required to spray dry detergent granules is to reduce the moisture in the slurry which is atomized in the spray drying tower, i.e., by reducing the evaporative load. An alternative method for making a high active detergent particle is by continuous neutralization in, for example, a continuous neutralization loop. There are continuous neutralization loops available to which relatively concentrated caustic can be added. Using a caustic solution which is about 50% sodium hydroxide allows reduction of moisture in the resulting neutralized surfactant paste to about 16% water. However, caustic of greater than about 50% solids cannot easily be added to existing continuous neutralization systems because the systems cannot reliably accommodate the viscous surfactant paste nor are the systems designed to accomodate the high temperatures necessary to handle concentrated caustic solutions. It has heretofore not been practical to use a continuous neutralization system to attain low moisture levels (below about 12%) in the paste so that free-flowing, high active detergent granules can be made from the paste.
The following publications describe ways to make free-flowing high active particles without drying, using surfactant paste, and made with a continuous neutralization system.
Japanese Patent 61-118500, Hara et al., laid-open Jun. 5, 1986, discloses a method for the manufacture of concentrated detergent compositions characterized by kneading the materials of the detergent composition continuously, and feeding these materials, which contain at least 30% by weight of surfactant, into an airtight-type kneader with a controlled pressure of 0.01-5 kg/cm.sup.2 G.
Japanese Patent 60-072999, Satsusa et al., laid open Apr. 25, 1985, discloses a production method for a highly concentrated powder detergent where sulfonate and/or sulfate is mixed with sodium carbonate and water in a high shear mixer, cooled below 40.degree. C., and then pulverized with a zeolite powder and other detergent components.
The use of polyethylene glycol and ethoxylated nonionic surfactants in granular detergent compositions is known in the art. For example, Japanese Patent 61-231099, Sai et al., laid-open Oct. 15, 1986, discloses concentrated powdered detergents containing (a) anionic surfactant, (b) polycarboxylic acid polymer or their salts, (c) polyethylene glycol, in certain percentages and weight ratios. The detergent also contains 0-10% by weight of a water-soluble neutral inorganic salt.
Japanese Patent 62-263299, Nagai et al., laid-open Nov. 16, 1987, discloses a method for the preparation of granular nonionic detergent composition by first kneading and mixing 20-50 weight % of nonionic surfactant at a temperature not above 40.degree. C., and 50-80 weight % of a mixture of zeolite, and lightweight sodium carbonate in a specified ratio, followed by granulation.
Patents exist which describe processes and/or surfactant compositions comprising viscosity modifiers such as polyethylene glycol and ethoxylated (E.sub.20-60) alkyl (C.sub.6-12) phenol. U.S. Pat. No. 4,482,470, Reuter et al., issued Nov. 13, 1984 discloses a process for reducing the viscosity of aqueous concentrates of anionic surfactants by adding a small quantity of a compound containing polyglycol ether groups; and the aqueous concentrates prepared thereby. Polyethylene glycol having a molecular weight of from about 600 to about 6,000 and ethoxylated (E.sub.20-80) alkyl (C.sub.6-12) are named as viscosity modifiers.
U.S. Pat. No. 4,495,092, Schmid et al., issued Jan. 22, 1985 discloses the addition of C.sub.8-40 alcohols, or C.sub.8-40 alcohols containing one or more hydroxyl groups and 20 moles of ethylene oxide and/or propylene oxide, to aqueous industrial anionic surfactants in order to significantly improve the rheological behavior thereof. The alcohols are apparently added in quantities of from about to about 15% by weight, based on the quantity of surfactant, whereupon the viscosity of the surfactant concentrate becomes at most 10,000 mPas at 70.degree. C.
U.S. Pat. No. 4,532,076, Schmid et al., issued Jul. 30, 1985 discloses an aqueous anionic surfactant concentrate with certain low molecular weight organic compounds as viscosity regulators, and a method of regulating the viscosity of highly viscous concentrates.
None of the above disclose the instant process for making high active detergent particles from the high active paste made by reacting alkyl sulfuric and/or alkyl benzene sulfonic acids with concentrated caustic in a continuous neutralization system in which polyethylene glycol and/or certain ethoxylated nonionics are added during neutralization in specified proportions.